A normally-closed electromagnetic fuel injection valve is provided with a pressure member such as a spring whose force is applied to a movable core including a valve plug in a valve closing direction. An actuator of the electromagnetic fuel injection valve includes an electromagnetic coil, a stationary core, and the movable core, and upon a current being supplied to the electromagnetic coil, an attractive force is generated between the stationary core and the movable core. By the attractive force exceeding a force of the pressure member exerting in the valve closing direction, the valve plug leaves from a valve seat to make a valve opening. When the current supplied to the electromagnetic coil is subsequently shut off, the attractive force between the stationary core and the movable core is set free. Thereby, the injection valve is closed by force of the pressure.
As a prior art related to the above-mentioned electromagnetic fuel injection valve, JP 2002-115591A discloses a method of controlling the valve closing speed of the movable core by supplying the current to the electromagnetic coil again just after once having shut off the current for the electromagnetic coil. This method can reduce an impact force of the valve plug against the valve seat at the time when the valve plug sits on the valve seat to close the valve, and thereby reduce bound of the valve plug due to impact on the valve seat.
JP2008-280876A discloses a method of, when a valve operation is done from a valve open state to a valve closed state, retuning the valve plug quickly to its initial position of the beginning of a valve opening operation, by energizing the electromagnetic coil just after the valve plug sat on the valve seat with a bound on impact. That is, thereby, the valve plug is applied with a force through the movable core in a direction opposite to the valve closing direction, so a rebound motion of the valve plug is suppressed just after the valve plug sat on the valve seat. This enables the valve plug to quickly return to its initial position of the beginning of the valve opening operation.
AS a recent prior art of reducing fuel consumption of an internal combustion engine, for example, a downsizing-engine is proposed. The downsizing-engine is configured to reduce exhaust emissions for downsizing purposes while acquiring an adequate output with a supercharger. According to the downsizing-engine, it can since reduce exhaust emissions, it also can reduce fuel pumping loss and pumping mechanical friction resulting in reduction of fuel consumption. Meanwhile, the use of the supercharger makes it possible to acquire an adequate output. In addition, a direct injection method is used to produce an intake air cooling effect. This makes it possible to suppress a compression ratio decrease caused by supercharging and achieve low fuel cost. As the downsizing-engine tends to decrease a cylinder diameter of the engine, it is anticipated that injected fuel night reach a cylinder wail surface. Split injection is proposed as a method of preventing the injected fuel from reaching the cylinder wall surface by splitting fuel mass per a one-time injection stroke into several injections.
As regards split injection, the related art of JP 2002-115591A discloses a driving method of the movable core only before the valve plug sits on the valve seat, but does not give special consideration to behaviors of the valve plug and its movable core after the valve plug sat on the valve seat with impact. After the valve plug sat on the valve seat, the valve plug and its movable core continue with their rebound motion on impact on the valve seat.
In particular, regarding in an injection fuel valve having a configuration that permits the movable core to have a relative motion with respect to the valve plug, the movable core continuously has the relative motion with respect to the valve plug after the valve plug sat on the valve seat with impact. Therefore, it takes some time for the movable core to come to rest, so it is necessary to allow a sufficient time interval between one injection and the next. Further, after the valve plug sat on the valve seat with impact, the movable core has the following behavior. That is, first of all, the movable core has a motion independent of the valve plug for a brief moment because of having a relative motion with respect to the valve plug to absorb the impact between the valve plug and the valve seat. Subsequently after a lapse of predetermined time, the movable core engages the valve plug again by working of a spring in a valve opening direction. However, at this moment, provided that a mass of the movable core and/or an impact speed of the valve plug are excessive, the movable core pushes up the valve plug, and thereby the valve plug may leave from the valve seat in spite of the valve closing operation.
As a method of reducing a time interval of the split injection, for example, JP 2008-230876A discloses of reducing the rest time of the valve plug by supplying an intermediate current just after the valve plug sat on the valve seat.
However, the above-mentioned prior arts don't give special consideration to timing of intermediate current supply and timing of intermediate current supply shut-off.
The present invention has been made in view of the above circumstances, and its object is to provide a drive device for a fuel injection valve capable of reducing a time interval between a first fuel injection period and a second fuel injection period subsequent to the first fuel injection period.